Slashdot videos: Now with more Slashdot!

View

Discuss

Share

We've improved Slashdot's video section; now you can view our video interviews, product close-ups and site visits with all the usual Slashdot options to comment, share, etc. No more walled garden! It's a work in progress -- we hope you'll check it out (Learn more about the recent updates).

holy_calamity writes "Engineers at Polytechnic University Brooklyn have discovered that digital snaps shorn of any metadata still reveal the make and model of camera used to take them. It is possible to work backwards from the relationships of neighboring pixel values in a shot to identify the model-specific demosaicing algorithm that combines red, green, and blue pixels on the sensor into color image pixels. Forensics teams are already licking their chops."

As even the cellphones are producing 3 megapixel images now, very few people need to be passing full-resolution originals around. If you scale the image down to a screen-usable 1 megapixel image, there's not going to be a lot of bayer mosaicking information still available.

Maybe so, but you still have the full size images on the camera. If someone were to get a hold of that they would be able to tell what camera took the images after a few weeks of intensive forensic study.

I might fool them by taking a picture of my Olympus and loading onto my Sanyo though. Seriously if you carried a suspect image around on a different camera you could now call an expert witness to show that it was not taken on this camera - and since the only other people who had access to the camera were the police it must be a frame.

Seriously if you carried a suspect image around on a different camera you could now call an expert witness to show that it was not taken on this camera - and since the only other people who had access to the camera were the police it must be a frame.

Feed your RAW images to photoshop, then hit NTSC color mode, then compress to jpeg. All their secret information is gone forever.
Only idiots would let this work.
and oh yea, those idiots didn't delete the Meta-Data anyway, cause they dont even know what it is.

or you could just use a camera with a Foveon X3 sensor [wikipedia.org]. there's no demosaicing involved since it employs 3 vertically stacked photodiodes (red, green, blue) at each pixel sensor to capture color information.

It does, but rather than narrowing it down to a particular model, it narrows it down to any digital SLR (and maybe other types) camera made by Sigma.

Add to that the fact that reducing the image size will probably get rid of the evidence, using a raw image and demosaicing on a PC will tell you what software was used instead of what camera was used, there are a lot of limitations.

On the other hand, most people do not know all this - then again, most people are unlikely to think of deleting the meta-data either.

Eric: Horatio, there does not look like there is any mosaicing information in this image.Horatio: Eric, that means the image was taken with a camera with a Foveon X3 sensor.Cally: Zeroing in on professional camera stores... I have an addressHoratio (menacingly): Eric, get on it.

I get more and more complaints that e-mails bounce: my mail server has a 10 MB per-email limit, and that should be enough. But many people copy the image from the camera, and then directly attach it to the e-mail. So I get many 3-4 MB sized attachments!

Quite often there are different manufacturers using the same sensor. Since this locks in the physical aspects of the sensor layout, I would expect the demosaicing algorithm to be basically identical across all these bodies.

After the sensor takes the RAW data, the camera processes the image (some noise reduction, curves, and compression) to get a jpg. Since this conversion would vary between manufacturers (or even RAW software) I'd imagine that the process would leave behind similar "fingerprints."

People like Ericsson Mobile Platforms (http://en.wikipedia.org/wiki/Ericsson_Mobile_Platforms) provide the same design to multiple handset vendors. As the industry progresses we can expect to see growing commonality.

There are photodesk editors with experience who claim to be able to identify the camera model, the lens used and the post processing software used to produce the jpeg / tif file. This is possible due to various characteristics that are introduced at each stage in the digital photographic process. Giveaways for the camera body used are the base resolution, any colour casts in the image, iso performance, dynamic range. For instance many Canon DSLRs are criticised for producing muddy greens in their images - especially at higher ISOs as the dynamic range is pushed to extremes. Then you can usually work out the lens - by the obvious field of view first, then the flaws in the shot - various lenses from various manufacturers have different flaws. For instance the 70-200 f/2.8 from Nikon has characteristic vignetting that can often be noticed even after post processing, then other cheaper lenses give various defects to the image such as chromatic aberation. The flaws in the image give away the body and lens. Also the sensor used gives certain image characteristics that are fairly easy to spot even to the keen amateur photogs eye - for instance telling the difference between a full frame sensor and a smaller APS sized sensor - the full frame image typically has a much smoother more film like attributes with less digital artifacts. Also the same can be said for post processing. This software usually leaves various characteristics - that remain with the image, and this varies for each different software vendor.

So this is all possible to a well trained human eye - don't see why it shouldn't be possible in software - but not sure of the real benefits of being able to identify this - as many photogs often leave the exif data - and that tells you everything.

I don't really see that as an issue. This seems like more of a "additional confirmation" tool that you'd use in the courtroom, rather than as a primary tool that you'd use to discover the identity of a person of interest.

As long as all the operations are carried out in scale you could likely determine the original 'finger print' since they would likely correspond. This could differ depending on the amount of alteration as well as distribution of the finger print across the pixels. Reducing the image to gray scale then using a separate function to interpret the color from there may be enough in some cases but YMMV.

...Of course, I wouldn't be surprised to learn that the distortion uniquely identifies the lens used...

Nah, not likely. Unless you knew exactly what the scene was supposed to look like, from that exact angle and everything (and even then it would likely be impossible), you just can't know what is a distortion from the lens and what is part of the scene. Unless, like, the scene happened to be a highly accurate checkerboard pattern. Then you can look and see what lines aren't quite straight and get some distortion information, but that would be tough.

I know software can correct for lens distortion if it has a distortion profile for a certain lens (which is probably made by shooting a checkerboard type pattern...), but knowing to move every pixel to the left one is a lot easier than knowing if every pixel was moved to the left one by the lens, if that makes any sense.

Put another way, it's easy to put soda in your mouth and have yellow stuff come out of your underbits, but very difficult to do the reverse.-Taylor

You really don't need anything so clean and nice as a full-scene checkerboard, to calculate a lot of lens details. Two or three moderate-length manmade straight lines that are at different angles should be enough. Like two edges of a table, a tall building, etc. That should be enough to give you the general curvature coefficients, which in turn would be pretty close to giving the right field of view. I don't think you'd be able to tell Sigma from Canon from Nikkor from Leica from Tokina from Zeiss glass.

So, if I shoot in raw mode, and then postprocess in software to get a jpeg, the demosaicing signature should merely identify the software, right?

Yes, they're just fingering the in-camera raw conversion to jpeg. Using external conversion changes the game.

There are comparisons of demosaicing algorithms used on the same raw image at several places on the net, such as http://www.rawtherapee.com/RAW_Compare/ [rawtherapee.com]. The software can make a huge difference, especially regarding moire and related artefacts. Most of the raw converters default to a much too aggressive approach for small scale features, in my opinion. As a result they often create chromatic moire in the JPEG, and accentuate the problem further by sharpening (to hide the softness of typical cheap lenses). This is clearly seen in the examples at the linked site.

Identical detectors on different cameras usually differ in the optical antialias filter used, which can affect their susceptibility to moire on sharpening. This may leave some residual information to allow the camera to be identified even with external conversion of the raw image. It would first be necessary to identify the demosaicing algorithm/software, so identifying the camera just from residual artefacts from the antialias filter would not be easy.

Of course, I wouldn't be surprised to learn that the distortion uniquely identifies the lens used...

Raw processing packages such as Bibble Pro also include a database of distortion characteristics for many lenses, including zoom lenses across their zoom range. Optionally, the image processing can compensate for the distortion for any recognized lens. Of course, the removal of distortion may leave a signature, which will perhaps allow both the lens and the software to be identified. This would not be a trivial task, of course, since "identical" lenses differ in their optical characteristics, and probably none exactly matches its nominal profile.

They don't have to. All they have to do is say they used forensics just like on CSI, and it shows it was taken by the same kind of camera you own. Sure, you can say there are a lot of them out there so it proves nothing. But you know who else says that? The bad guys on CSI, and their smug, latte drinking lawyers. Always demanding warrants and to be released if they aren't being charged with anything! EVIL

And you know that 1x1 pixel is all the evidence we need. You see, that pixel represents a single atom, which has bands of electrons, each with distinct spins, each of those with unique quantum signatures all the way up to other dimensions in other universes, all tied together with string theory back to the original untouched photograph.

You may sign the confession now or we will get a court order to further examine the evidence...

"Chief! We only got a 1x1 pixel area of the jpeg of the criminal!" "Okay take it downstairs to Abby and McGeek to check it out".

[Wiggly Lines]

"Yeah Chiefy it was pretty easy. We zoomed in on the 1x1 pixel image and we got this picture of the criminal which was inside there. And we got the model of camera he used too, an Motorola RAZR Smartphone." "Yeah Chief, there's only been ninety jillion RAZR phones made, so we hashed the 1x1 pixel image and g

The bad guys on CSI, and their smug, latte drinking lawyers. Always demanding warrants and to be released if they aren't being charged with anything! EVIL

The only EVIL on CSI shows is the way the motherfucking cops use extortion.

"You don't want to give up privileged information on this guy? Fine, we'll be back with a warrant. Of course, we may have to dismantle your office for a couple of weeks to do a thorough search. What does a couple of weeks mean to your business? You do understand, don't you, that when we seize (God, how those bastards love the word "seize") your computer, our clumsy techs might return it with some important files no longer readable? So sorry.... Oh, yes, ma'am, that's the perp we were inquiring about. Thank you for your cooperation."

The stuff you see on CSI and other similar crime shows is grossly unrealistic. It's actually so unrealistic that judges typically give a bit to jurors when they're in the panel that they should not put cops onto a standard compared against these shows (no one would ever get convicted). One of my judges used to put it something like this: "You need to understand the difference between reality and television. On these shows, the investigators find a footprint with blood, match it up to a boot tread, then f

That's not the purpose. Knowing the photo was taken with a D70 eliminates all the zillions of cameras out there that aren't D70s. It's like knowing that a bank robber is a 6' tall blue-eyed blond male.

So what if they can identify the make and model of camera. I own a D70. There are 300 billion d70 out there. Good luck on tracking a picture to my camera.

RTFA:

While many people own the same camera models, Pollitt believes that this technique can still be used forensically. He says that because digital cameras have a shelf life of only 18 months, this can help to narrow down when and where it was sold.
Just because it won't immediately narrow it down to a single suspect with perfect accuracy doesn't mean it won't be helpful in investigations.

It's clearly a technique for child porn investigations. If you have a suspect who owns the same kind of camera you determined was used to take the photo in question, which the investigators most certainly didn't get from the photographer them self, you can know whether to search for more evidence or to eliminate them from your suspect list.

Most people who do this kind of thing are not necessarily going to realize this is possible, so aren't going to think of the obvious solution, which is to borrow someone

Maybe I'm naive, but it took this long into the discussion thread for somebody to explain why this is even a story. I hadn't thought of that (because I'm a decent human) and I guess everyone else *thought* it, but were a bit uncomfortable stating what is otherwise totally obvious to most folks.

While many people own the same camera models, Pollitt believes that this technique can still be used forensically. He says that because digital cameras have a shelf life of only 18 months, this can help to narrow down when and where it was sold.

1) RE: Originally sold. My 7 year old carries a 4 Mpixel camera that we bought at a yard sale, which that guy bought off E-bay. "They" might be able to tell that the picture of interest was taken by a camera originally sold at a WalMart in upstate New York, not that it was taken by a kid in Winnipeg.

2) RE: "shelf life". Of the 25+ cameras that my extended family own, none are newer than 18 months. Most are 2-3 years old.

So what if they can identify the make and model of camera. I own a D70. There are 300 billion d70 out there. Good luck on tracking a picture to my camera.

RTFA:

While many people own the same camera models, Pollitt believes that this technique can still be used forensically. He says that because digital cameras have a shelf life of only 18 months, this can help to narrow down when and where it was sold.

Just because it won't immediately narrow it down to a single suspect with perfect accuracy doesn't mean it won't be helpful in investigations.

I suspect this would be more useful as a way to exclude cameras that wouldn't have likely taken the photograph. If you have 100 suspects, and can mostly exclude 95 of them on this basis, that's useful.

So what if they can identify the make and model of camera. I own a D70. There are 300 billion d70 out there. Good luck on tracking a picture to my camera.

Its useful the same way knowing the car that raced away from the scene of the crime used a particular tire, with a particular wheelbase. Or that a bullet was fired from a particular make of gun.

Neither will positively identify anyone, but if you were already a 'person of interest' in a long list of people peripherally related to a case that detail might put you on a MUCH shorter list if it comes up that you have that model. Plus its useful when they are asking a judge for a warrant. Judges really like specificity with warrants... A "We want to search his home and car for a Canon Powershot X"; he blogged here about buying a Canon Powershot X, he was caught on this surveillance tape leaving the scene carrying an indistinct object, the dimensions and shape of which are consistent with a Powershot X, and we know the photos in question were taken with a Canon Powershot X"... that's got a lot more weight than... "We want to search this guy for a digital camera, because a witness said he owns a camera, and he was caught on tape holding an indistinct smallish object which could be a camera, oh... and the photos we're interested were taken with a camera."

A reasonable person would view the second as a complete fishing expedition, based on no evidence, practically everyone has a camera and he could have been holding anything on that tape. The first request is specific - the photos of interest were taken with that model, and there is reason to beleive the person HAS that particular model, and that he had it with him on the that tape. Sure it could be a coincidence, but a warrant for that particular camera if he has one to check it out, might not be unreasonable.

Its also not unlikely that they can pair photos to a particular camera if they have both on hand due to micro-scrathes and other unique lens defects... the same way they can pair laser pritners to printed output.

As for laser printers, they can be identified uniquely because, on each page, they surreptitiously print a binary code (serial number, at least) in very small, light yellow dots. Yellow on white paper is nearly imperceptible. Wiki it for the whole story, including how to find and interpret the dots.

Yes, but even without that, you can match a printout to the drum, based solely on defects due to wear in the printer. The printer/paper equivalent of ballistics matching a bullet to the barrel it was fired throug

Depth of field isn't a question of better or worse, you know, it's just different. If you want to poke at that story, you might just point out that a the limited image size makes the comparison pointless. These days, cheap digital cameras make incredibly expensive pro cameras more useful for either flexibility or niche markets (like >13" prints). That doesn't mean professional cameras aren't worth it, just that they're not worth it for everything.

I don't disagree, the point that I was trying to get at was that the OP's conclusion didn't jive with the site. I've never owned an SLR and I'm pretty sure the majority of the photo quality problems I've had are the fault of the person holding the camera.

My wife and I have two point and shoot cameras, a Nikon and an Olympus. We also have a Pentax dSLR.

Looking at the images at 100% scale and you can see a tremendous difference in the amount of noise in the backgrounds. That is mostly caused by the smaller size of the CCDs and the quality of the sensor itself. Plus, the higher end cameras have far better noise reduction software built in.

Depth of field is EVERYTHING to taking pictures. By using a long lens and a large aperture, bars around zoo cages disappear, the annoying crowd behind the bride also disappears, or that person just standing behind your subject gets just the faintest blur so your eye is drawn to the subject. Or use a small aperture and everything is brought into crisp focus.

Then there is being able to use higher quality optics. I recently used the Pentax camera to take some campfire scenes using a 50mm(film) lens set at 1.4f. I was able to take clear, handheld images around the campfire. Try that with a point and shoot.

I'm not knock the PS cameras. I use them when I'm riding my motorcycle to get action shots of those I ride with. That would be impossible with a dSLR or SLR camera, they are just too big and bulky.

But if someone wants to take high quality snapshots to share, nothing beats a dSLR. Pricey, yes. But well worth it for the serious photographer, be they professional or hobbyist.

Looking at the images at 100% scale and you can see a tremendous difference in the amount of noise in the backgrounds. That is mostly caused by the smaller size of the CCDs and the quality of the sensor itself. Plus, the higher end cameras have far better noise reduction software built in.

In addition to noise, the small digitals show lots of other image degradation as compared to a dSLR. They lack sharpness and have issues with distortion, color accuracy and chromatic aberration. The ultimate source of all of those issues is the glass. You simply can't get the same level of quality out of a half-inch lens as out of series of two-inch lenses (assuming similar technology applied to both).

I just shake my head at the ever-increasing megapixel numbers on compact digital cameras. I know they're great for marketing, but for the camera owners they do nothing but produce bigger files, with no better image quality than if they'd had a smaller pixel count. Once you get beyond the resolution of the glass, there's just no point in adding more pixels.

I just read the Haselblad/Canon comparison, though, and I have to point out that the Canon G10 is not what most people think of when you say "cheap digital". It's not an SLR, but it's close, with larger, better glass than most P&S cameras and a larger sensor. 15MP is a bit much for those lenses and that sensor size, but it's not that crazy.

You missed the point. He said that every sensor is different, so each needs to be adjusted as desired. Claiming one is "better" because of the yellows is a) not what he said and b) irrelevant to the discussion.

As for the depth of field, again you get it wrong. Depth of field is adjustable - one camera or image isn't better or worse if shot with a particular depth of field. What he said was that the Blad pictures were shot with a narrower depth of field and that his experts were able to discern which we

You can do all sorts of stuff to an image that would shot holes in this technique. Resize (shrink, or grow and reinterpolate), apply a filter (curves, b&w or sepia would be easiest but there are others). Hell put it through an artistic filter. Still at 90% accuracy, in most cases, I wouldn't even bother!

> Of course someone who is stripping the exif data will never resize the image and run> some sharpening over the image just to cover their traces, right?

Some will, some won't. Criminals are notoriously careless and stupid.

> Yep, this one was taken by a Canon Powershot A510 of which only 5.7 million were sold.> We also know that this particular model was either sold in North America, Japan, Europe,> Africa, Australia, South East Asia and South America. That should narrow it down.

Yes. Of the 18 initial suspects only two own that camera. Concentrate your investigation on them.

I can only see this, in a positive light, as uncovering fraud or deception -possibly even supporting a claim as to the veracity of a witnesses' testimony to photographing a crime- instead of this being used in a nefarious way. Although, once the algorithm is well understood, certain 'non-well-intentioned' organizations or individuals will use this for evil instead of good. But in the meantime, how would this worry the average digital shutterbug?

Could perhaps be used for prosecuting people who take photographs in "forbidden" areas, such as evil people who dare to take pictures in the DC Amtrak station, on the Pentagon reservation, and other such areas. I can't quite figure out how this would play into it though.... And of course as far as I know nobody has (yet!) been prosecuted after the fact for such photographs.

Except with typewriters and gun barrels there are physical nuances that leave unique markings on bullets/letters. This just identifies the model, and even that's degraded as the image goes through various software manipulations, as other posters pointed out. It may help reduce the population of digital camera owners in question, but it doesn't seem like the kind of evidence forensics teams are "licking their chops" over.

I have a friend who is so paranoia about leaving personal data on the Internet he doesn't even use his own name as login name on his iMac. Don't let him hear this or I will never get any pictures from him by mail anymore!

This sounds like the equivalent of "registering" typewriters with the government in nations once behind the Iron Curtain. It is no different than obtaining ballistic signatures from firearms at the manufacturer level. Yet one more reason to distrust governments.

Luckily for anarchists, alleged terrorists and people who take pictures of cops thugging out on citizens, today's basic digital camera costs nearly as much as dinner for two at the local fast food joint. "Disposability" is your friend.

At first blush this struck me as similar to the printers that revealed a specific device by a faint set of dots printed on each piece of paper. On further thought, it occurs to me that the difference would be that the dot-tracking was shady where-as this is a triumph of statistical observation. The former being slimy and the latter sheer brilliance.

I better sell my Nikon D300. They'll be able to trace it back to me. Or one of the other gazillion people who also bought one. Hmm... on second thought...

you're missing the point.
there usually are other factors in play in any investigation. having only the camera make to go by is useless, but not so if you've managed to narrow - through other criteria - your suspect list down to 10.

Closer examination of my car revealed the tires leave marks on the ground if it soft enough or if I come to a sudden stop or extreme speed. This could give away the type of car you own to anyone. News at 11.

Um, stripping and faking EXIF are trivial anyone with a hex editor and a little knowledge can do it. In fact when a new camera comes out it's fairly common to fake the EXIF of a previous model to use the RAW converters before a model specific one comes out. Oh and the scientists were talking about identifying a photo with the EXIF data stripped.